In a known electric power system, as shown in FIG. 8, “a radial system” in which a large power plant 91 is a top and demanders 92 are a base, is fundamental. In FIG. 8, to secure a plurality of electric power transmission systems, “a loop system” is introduced in some part. This kind of an electric power system is configured, as a single system, in a broad area (for example, several tens of thousands km2) and large scale (several tens GW).
In contrast, recently, attention has been paid to a grid-connection type distributed electric power generation system (refer to, for example, Patent Documents 1 to 3 and the like) with solar generation and a fuel cell. The distributed electric power generation system of a system collaborative type is ordinarily built in an end region or a local region near to the end region of the known radiated electric power system and is premised on interconnection with the electric power system.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 6-327146    Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2004-15882    Patent Document 3: Japanese Patent Application Laid-Open Publication No. 2002-44870